AstraZeneca's board is facing increased pressure from shareholders to re-open talks with Pfizer, even though it would be unable to push for a higher price.

The British drugs giant swatted away the US predator’s final £55 a share offer on Monday in a move that all but guaranteed its independence. But investors have split over the move, which led Astra shares to drop to £42.

Now Legal & General – its sixth-largest shareholder with a 3.5 per cent holding – has written to the board telling it to re-engage, according to reports.

Pfizer takeover: Legal & General has written to AstraZeneca's board telling it to re-engage

It comes after AXA – the third-biggest investor – told the Mail the decision to reject Pfizer’s offer was ‘not acting in our interests’.

Schroders and Jupiter, both major shareholders, have also publicly criticised the board’s decision.

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But Threadneedle, its 15th-largest investor, yesterday came out in support of the board, saying the company was a ‘strong standalone business with a good product pipeline’ that had ‘made notable progress under Pascal Soirot’.

Even if it wanted to, Pfizer could not raise its final offer price because of legal constraints in the takeover rules.

The Viagra maker also cannot significantly increase the amount of cash it is offering because it needs to pay in its own shares in order to shift its tax base out of the US.

Astra shares yesterday rose 111.5p to 4420p and this morning were down 38.75p at 4381.25p.